Electric recording apparatus employing liquid developer

ABSTRACT

A method and apparatus for generating imagery in which information from either an original document or an electronic input is placed on paper or other suitable record medium by the use of control element(s) which establish an electric field adjacent to the record medium; the recording element(s) being immersed in a liquid.

United States Patent lnventor Appl. No. Filed Patented Assignee RichardA. Fotland Cleveland, Ohio June 4, 1970 Nov. 23, 1971 HorizonsIncorporated, a division of Horizons Research Incorporated Cleveland,Ohio ELECTRIC RECORDING APPARATUS EMPLOYING LIQUID DEVELOPER 8 Claims,11 Drawing Figs.

05. Cl. 346/74 E, 355/3, 355/8 lnt. CL G033 13/00 Field of Search 346/74CH,

74 E, 74 P, 74 R, 74 ES; ass/3.4, s, 10;204/1s|, 30o

[56] References Cited UNITED STATES PATENTS 2,932,548 4/1960 Nau et al.346/74 ES 3,270,637 9/1966 Clark 355/10 X 3,383,993 5/1968 Yeh 355/10 XPrimary Examiner-Robert L. Richardson Allorney- Lawrence 1. FieldPATENTEDmv 23 Ian SHEET 2 OF 2 L INVENTOR Richard A. For/0nd FIG. IO.

ATTORNEY ELECTRIC RECORDING APPARATUS EMPLOYING LIQUID DEVELOPER Methodsand techniques for producing visible images from an electrical inputhave been known and practiced for many years. Facsimile recordersemploying special papers are in wide use. The image is formed eitherthrough the electrolytic development of a color or through the use of anelectrical discharge to vaporize (blast-off) an overlayer.

Another widely practiced technique involves a corona discharge from afine stylus spaced a very short distance above an insulatingsurface-generally a paper whose surface is coated with an insulatingthermoplastic film. This method of recording is well described in thepatent literature, including the following US. Pats. Nos. 2,894,799,3,064,259, 3,068,481, 3,131,256, 3,208,176, 3,217,330, 3,289,209,3,383,697, 3,384,898, 3,409,899, 3,417,404, 3,434,157, 3,471,861.

Another method of generating an image is described in my U.S. Pat. No.3,121,375 (Contrography).

A basic difference between these known techniques and the presentinvention is the presence of a liquid at the recording stylus in theprocess and apparatus of the present invention.

In the present description, a variety of apparatuses are described inwhich the use of a liquid medium disposed between the electrodes and therecord medium, instead of air, produces several significant advantagesincluding the following:

1. The realization of much higher resolution than obtained with an airelectrical discharge technique;

2. A significant increase in recording speed due to the rapidity withwhich the stylus discharge forms the image (higher modulation rate ofthe potential applied to the stylus);

3. The recording and development step occur simultaneously or nearlysimultaneously, thus simplifying the apparatus utilized for implementingthis method of recording.

The present invention will be more fully understood from thedescription'which follows taken in conjunction with the drawings inwhich:

FIG. I is a schematic view of one kind of recorder which may be used;

FIG. 2 is a fragmentary view of a modified stylus which may be used;

FIG. 3 is a fragmentary view partly in section of a modification inwhich a plurality of styli are used;

FIG. 4 is a plan view of a record medium passing through the apparatusof FIG. 3;

FIG. 5 is a modification showing a computer output generated copyingapparatus;

FIG. 6 is a further modification utilizing a line optical input;

FIGS. 7, 8 and 9 are views of a further embodiment of which FIG. 7 is aside elevation, FIG. 8 is a view of the embodiment of FIG. 7 lookingtoward the left side, and FIG. 9 is a schematic wiring diagram;

FIG. 10 is a further modification, shown schematically; and

FIG. 11 shows still further embodiment for high-speed recording ofelectrical inputs.

In the figures the use of primed and double-primed notation indicatesthat the structure equivalent to similar structure identified by thesame numeral in an earlier figure (see trough 12 in FIG. 1, 12' in FIG.10 and 12" in FIG. 11).

EXAMPLE 1 Example 1 is best understood with reference to FIG. 1. Therecorder shown in FIG. 1 includes a medium 10 upon which the record ismade. This recording sheet 10 may consist of a clear plastic film baseor any type of paper. The recording medium 10 is guided through a trough12 containing a liquid developer 14 by the use of rollers 16. Anyconventional means (not shown) may be utilized for advancing the recordmedium 10 through the liquid developer 14 contained in trough 12. Theweb may be continuously drawn through the recording system or the drivemay be intermittent; for example, if a single frame at a time is to berecorded. Excess developer is removed from the web by squeegee rollers18. Residual developer solvent remaining on the web is removed by a warnair plenum 20. The recording stylus 22 includes a stylus tip 24 whichmay consist of a coarse wire sharpened to a tip width of 2 to 3 mils, orthe tip 24 may be spherical with a radius of about 5 to 20 mils. Therecording stylus is moved over the surface of the recording sheet, thestylus tip contacting the recording surface, by an electromechanicaldrive 26. A modulated source of electrical potential 30 establishes anelectric field between the stylus 22 and a conducting counterelectrode28.

The electromechanical drive which positions the stylus the recordingmedium may be any one of a variety of drives well known to the art, forexample, an X-( recorder or servo drive to position the stylus in twodirections or a high-speed recording pen motor or any other suitableknown mechanism.

A developer was formulated by milling carbon black in a petroleumsolvent (Isopar G manufactured by Humble Oil and Refining Company). Thisdeveloper was diluted with the solvent until the solids concentration(by wt.) was 0.5 percent. Other liquid developers, such as thosedescribed in U.S. Pat. No. 3,259,581, were also effective in theexamples which follow.

With the developer described above, dense thin lines were recorded atstylus potentials in excess of 200 volts; the recording stylus 22 beingnegative with respect to the counterelectrode 28. The line width couldbe varied from V4 to 10 mils, depending upon the geometry of the styluspoint and to a lesser extend upon the applied potential. Dense lineswere recorded at the highest velocity provided by the electromechanicaldrive or 200 inches/sec. The optical density of the line increased up tothe maximum potential applied of 1 ,200 volts.

FIG. 2 is a fragmentary view showing a modified stylus which may be usedin which a large tank of developer is not required. By employing themodification herein, means are provided for rapidly changing thedeveloper so that, for example, different colored developers may berapidly introduced near the recording stylus to change the image color.In this figure, the recording medium 10 is once again supported on aconducting counterelectrode 28. The recording stylus 22 is supported ina cylindrical tube 32 which is open on the bottom and closed on the top.The tube-stylus assembly is positioned by the electromechanical drive26. Potential is once again supplied by the modulated voltage source 30.The interior space of the cylinder 32 contains the developer solution 14which is recirculated through inlet tube 34 and removed at outlet tube36. The liquid developer is continuously recirculated through areservoir by a solenoid-operated valve and pump (not shown in thefigure). By employing electrically operated solenoid valves, it ispossible to switch from one color developer to a different colordeveloper in a time period of less than 1 second. Thus, not only may'thedensity of the image be controlled by the voltage supply 30 but thecolor may also be selected at will.

EXAMPLE 2 The device sketched in FIG. 3'illustrates an apparatus forrecording alphanumeric or other symbolic information. Here, rather thanusing a single stylus as shown in FIG. I, seven styli 22 are employed.By pulsing these styli at the appropriate time, alphanumeric characters(seven elements high) are formed. Referring to FIG. 4, which is a topschematic view of the recording system, showing the recording film 10 orpaper and the styli 22 which are identified by the letters a through g.These styli are mounted in a recording head 40 which may or may not bemounted on an electromechanical transducer or rapidly revolving drum forthe purpose of scanning across the film or paper. The styli pulsegenerators and logic are contained in an electronics package 42. Thetips of the styli are, of course, submerged in the recording liquid (notshown).

The operation of this recorder may be best explained with reference toFIG. 4. In this drawing, the film or paper base is moving rapidly fromleft to right. The character A is shown formed here.

The styli may, if the character size is to be reasonably large (forexample, of a size suitable for direct viewing), be arranged in avertical array. In this case, the letter A would be formed by brieflypulsing electrodes C, D, E, F and G followed in sequence by pulses onBD, AD, BD, and then CDEF and G. The time interval between each pulsewould be characteristic of the velocity of the web and the distancebetween the character elements in the direction of web travel. The stylishown in FIGS. 3 and 4 are staggered in such a manner that the distancebetween adjacent styli is increased over the distance which would bepresent if the styli were arranged in a vertical row. This minimizescrosstalk between styli, eliminates the possibility of voltage breakdownbetween styli, and simplifies the mounting and alignment of the styli.These advantages are important only if very small dimensions arerealized; for example, when it is desirable to create alphanumericcharacters mils or less in total height. In the case of staggered styli,appropriate electronic logic, well known in the art, must be employed sothat the appropriate time delays are utilized to fonn desiredcharacters.

It will be understood that, if desired, the styli may be continued,extending completely across the web in a direction either orthogonal orinclined to the direction of web travel. Proper commutation must beprovided in order to select the printing styli out of the large numberof styli present.

EXAMPLE 3 The apparatus of FIGS. 3 and 4 may be modified to generate, ata very high rate, alphanumeric characters from computer output. Anexample of a computer output generated microfilm apparatus is shown inthe schematic of FIG. 5. This figure shows the transparent plastic base10' in web form, the counterelectrode 28', and a scanning wheel 44.Embedded in the edge of the scanning wheel are four styli assembliesspaced 90 along the circumference. Each styli assembly consists of sevenstaggered styli of the type shown in FIGS. 3 and 4.

The modified apparatus is compatible with presently available computeroutput microfilm recorders of the type employing an optical intermediatesuch as a cathode-ray tube or laser diode matrix. Thus, the film I0 is16 mm. and the recording is formed over a A inch width on this film. Thecharacters on the film are reduced so that they are suitable for normalviewing at 26X magnification. On the film, the characters are 3 mils inheight and 4 mils wide. The width of each incremental recorded area,corresponding to a single discharge from a single styli, is 0.4 mil.Since four styli assemblies record over a Vzto inch area along thecircumference, the recording disc diameter is 0.64 inch. The recordingrate is 10,000 lines of alphanumeric characters per minute or 166 linesper second. The peripheral velocity of the scanning wheel 44 is then 83inches per second and the disc rotates at 2,500 rpm. The entire assemblyis, of course, submerged in liquid developer of the type described inexample I. In each line there is space for 132 characters correspondingto a packing density of 260 characters per inch. During operation, thedevice generates 22,000 characters per second Since the image elementspacing is approximately 0.4 mil, the maximum pulsing rate at the styliis 220,000 pulses per second.

Since the recording is directly electronic, there is no need to utilizeintermediate optics in forming the image. The image is recorded on alow-cost transparent base. The only complexity over more conventionalCOM recording techniques is the requirement for additional logicnecessary for the proper formation of alphanumeric characters since therecording styli are staggered in the recording head.

In a further modification for generating computer output microfilm, thescanning wheel may be replaced by a highspeed pen motor drive. Therecording stylus assembly is then mounted on the top of a pen connectedto a high-speed pen motor. Many of these pen motors have mechanicallinkages so that the scan is rectilinear rather than over an arc. Over ascanning distance of one-half, the required 166 scans per second arewell within the state of the art.

EXAMPLE 4 This example describes a recording system employing an opticalinput. In some respects, examples 4 and 5 are similar to devicesdescribed in US. Pat. No. 3,121,375. The major difference is that theexamples in the patent indicate the developer manifold placed on theside of the recording web opposite the control electrode (with theexception of the capillary manifold control). In the embodimentdescribed in this example, the control electrode is immersed in theliquid developer and this electrode is in contact with the surface beingrecorded upon.

The apparatus shown schematically in FIG. 6 includes a line opticalinput to control the potential at styli, causing a visible image toappear on recording paper 10. In this figure, 28 is a counterelectrode.The liquid developer surrounding the tips of the styli is not shown inthe figure. The recording head assembly consists of a glass plate 50containing a cylindrical cavity 52 near the top surface. A photocathodelayer 56 is deposited on the surface of the glass bore. Thephotocathode, which may be of the cesium-antimony type, is of sufficientthickness to be electrically conducting. An electrical connection 58 ismade between the photocathode and a DC power supply 60. A number ofstyli 22" are embedded in the glass recording head 50. These styliconsist of Kovar pins 5 mils in diameter spaced on l0-mil centers. Thespacing determines the resolution in the direction across the paper; inthis case equal to lines per inch.

In operation, an original document is moved past a l0-mil wide slit at arate equal to which the copy paper 10 moves under the recording styli22". Means, not shown in FIG. 6, are provided for imaging theilluminated original onto the photocathode. Optics effective forcarrying out this imaging are shown in FIG. 1 ofU.S. Pat. No. 3,121,375.

The copy device shown in FIG. 6 is negative working. Thus, whenillumination reflected from a white area of the original strikes thephotocathode 56, electrons are emitted. These electrons are collected bythe electrode connected to the stylus 22", causing the potential of theelectrode to be driven negative with respect to the counterelectrode 28.The presence of a voltage at the paper results in the deposition ofdeveloper particles.

The effectiveness of this technique is illustrated by the followingcalculations. The capacity between a single styli and thecounterelectrode is 10" picofarads, assuming a paper thickness of 3mils. A total charge of 5 [Ly-COUIOI'IlbS per element is transportedfrom the photocathode to the stylus to raise the pin potential 1,000volts. Since there are approximately 10 discrete image elements per copysheet, the total charge transported per copy (assuming the sheet wastotally printed) would be 5 coulombs. At a copy sheet speed of 2inches/sec., the copy is formed in 5 seconds and hence the total maximumrecording current is 1 ampere.

The instantaneous potential of a recording styli is equal to 1/Cf idt,

where C is the capacity and i is the charging current. Since thecharging current is independent of voltage, the charging time is merelyequal to the product of the potential difference through which anelectrode is charged and its capacity to the counterelectrode divided bythe charging current per stylus. Since the charging current of a singlestyli during operation is near I nanoampere, the charging time is 5msec. Thus, the maximum recording rate at the minimum current levelrequired for operation is 200 elements per second. Since there are I00recorded elements per inch, the maximum recording speed, at the lowestoperational light level, is 2 inches/sec. At higher illumination levels,the recording speed may be propor- R. FotlanlifJ. Ap Phys, 3 i', U53?TEEDI per lumen.

tionally increased since the charging current is proportional toillumination.

The sensitivity of a typical cesium-antimony photocathode is 20aa/lumen. In order to generate the required I a. charging current, 0.05lumen is required at the photocathode. Since the efficiency of theoptical system is near 5 percent, the total luminous flux from thescanned area on the original must be I lumen or greater. The area of thelO-mil scanning slit (8% inches wide) is 0.0006 ft. Thus, theillumination level at the slit must be 1,600 ft. candles or greater.This illumination level is easily obtained with simple condensing opticsimaging a tungsten halogen lamp onto the slit.

EXAMPLE 5 FIGS. 7, 8 and 9 schematically illustrate another modificationwherein the imaging concept described herein may be controlled via anoptical input. In this embodiment, the potential at the styli ismodulated by a photoconductor. In FIGS. 7 and 8, the copy paper or film10, the counterelectrode 28, and he liquid developer 14 are disposed asshown. An array of conducting elements and photoconductors are depositedupon a recording head employing photoresist techniques well known tothose skilled in the art.

The recording head 60 consists of a glass or ceramic substrate 62.Deposited directly upon this substrate are a series of conductingstripes 64. These stripes are 5 mils in width and spaced uniformly onlO-mil centers. A single broad stripe 66 of photoconductor material isdeposited over stripes 64. The particular photoconductor chosen dependsupon the specific application. If a high-sensitivity and relativelylow-recordingspeed system is desired, cadmium sulfide or cadmiumsulfoselenide may be deposited to form the photoconductor. In order torealize high recording speeds, a fast-response time photoconductor isrequired. Amorphous selenium falls into this category. The manner ofpreparing such a film and its characteristics are described in theliterature. Two conducting electrodes electrodes, 68, 69 are depositedover the photoconductive film. One of these electrodes 69 must besemitransparent so that the incident illumination can irradiate thephotoconductor, while the second electrode 68 may be semitransparent oropaque. Power supply 70 is connected between these two conductingstripes. As seen in the circuit diagram of FIG. 9, this arrangementprovides a bridge, two arms of which are composed of the photoconductor.Upon illuminating one of the arms of the bridge, the potential at therecording electrode 64 rises, thus causing an image to forrn on therecording sheet.

This recording W252i; 7 when A fabricated employing amorphous seleniumas a photoconductor, requires illumination levels similar to thoserequired for example 4 since the sensitivity of an amorphous seleniumlayer is close to 20 a.

EXAMPLE 6 This example is an embodiment which provides for twosignificant advantages over previous examples. The imaging system issketched in FIG. 10. Rather than develop the image directly on a paperor film 10 (as shown in previous examples), the image is formed on theinsulating surface of a transfer roller 74. This roller is uniformlycoated with an insulating film 76 having a thickness in the range of Ito ID mils. A preferred coating material is a vitreous enamel because ofits high strength, high abrasion resistance, and ease of cleaning. Theimage placed on this insulating surface 76 by the control recording head72, which may consist of any of the previously shown types of recordinghead, is transferred to the copy paper 10 by a transfer roller 78. Inorder to effect efficient transfer, a high electrical potential may beconnected between rollers 78 and 74 to aid in electrostaticallytransferring the image from the drum to the paper. Residual image isremoved from insulating surface 76 by a cleaning brush 80.

One advantage of this approach is associated with a reduction inbackground levels on the copy sheet. It has been found that when thecopy sheet is immersed directly in the liquid toner, small amounts ofdevelopment liquid are carried out of the development bath by the sheet.As the developer solvent evaporates, developer particles are left on thesheet which results in a slight background level.

This background level may be reduced by predevelopment immersion of thecopy paper into a bath of solvent not containing developer pigmentparticles.

The preimmersion serves to imbibe pure solvent into the paper, thusminimizing the pickup of pigment containing solvent during thedevelopment operation. In the device of FIG. 10, the paper background isextremely clean since there is very little solvent carryover by the hardinsulating surface 76.

Another advantage of this embodiment is associated with registration inpreparing full color copies. By employing color separation filters andthree recording heads, the recording and imaging systems describedherein may be readily adapted to form color images. An example of thecolor separation optics required is shown in FIG. 5 of US. Pat. No.3,121,375. Any of the previous techniques may be employed in formingcolor images by mrely utilizing several heads and different coloreddeveloper pigments. In a three-color system, three separate recordingheads are required. Although these heads may be positioned relativelylose to one another along the copy sheet, it is impossible tosuperimpose the heads since the liquid developers must be spatiallyseparated along the web. If a color image is formed by recordingdirectly upon a paper, the registry of the image in the direction ofpaper travel is dependent upon the accuracy of the optics, consistencyof spacing in the recording heads, and uniformity of the paper geometryas the paper moves through the three recording stations. Since paper issubject to stretching and dimensional changes, an improvement inregistration is observed if the colored recording is carried out byspacing three heads around the circumference of a transfer drum. Sincethe geometry of the drum is invariant, accurate registration isobtained. The full color image, in registry, may be subsequentlytransferred to a copy paper.

EXAMPLE 7 FIG. 11 shows a configuration of high-speed recording ofelectrical inputs. Shown here are copy sheet 10 which passes under aprinting roller 82; this roller also serving as a counterelectrode.Development is carried out in a meniscus formed between the copy sheet10 and a roller 84, the bottom half of which is immersed in a liquiddeveloper reservoir 12". Roller 84 rotates with a surface, velocityhigher than printing roller 82 to continuously replenish and supplyliquid developer to the meniscus. Scanning across the paper i carriedout with the aid of a high-tensile-strength wire 86, upon which aremounted conducting recording styli beads 88. Thirty-gauge stainlesssteel wire has been found satisfactory for this application; the beadsbeing formed by cementing 30-mil diameter stainless steel balls onto thewire. The wire passes over pulleys 90, one of which is driven by ahigh-speed synchronous motor 92. A modulated recording signal is appliedbetween conducting roller 82 and the recording wire 86 from themodulated power supply 94. The recording beads contact the surface ofthe paper and are mounted along the scanning wire at 8 VZ-inChintervals. In one embodiment of this device, four balls are spaced equaldistances along a 34 inch endless wire loop. The drive pulleys are 3inches in diameter and the drive motor revolves at 12,000 r.p.m. At thisrate, a given ball scans across the Bk-inch wide copy sheet at avelocity of 1,800 inches per second and generates 225 scans per second.The scans are on IO-mil centers and thus the time required to generate asingle copy is 5 seconds. Since it is desired to have approximately 800resolvable elements across the sheet, the recording bit rate is [80,000bits per second. The modulator band width must then be approximately I00kHz.

This high-speed facsimile Ewing technique has the advantage ofcompactness, high recording rate, and the capability of employingconventional papers.

In summary, this modification in which the recording stylus anddeveloper are on the same side of the recording media and the stylus issubmerged in developer appears to offer significant potential in anumber of areas. The input may be either optical or electrical. Theprocess is relatively simple. Line widths as narrow as one-fourth milhave been obtained, thus indicating a potential for formingmicroimagery. The writing speed, on film, is over 120 inches per second.The maximum modulation rate and writing speed observed have been limitedby the apparatus presently available rather than the process itself.

I claim:

1. A recording apparatus including at least one recording stylus, meansto move a recording medium relative to said stylus and to maintain oneend of said stylus in physical contact with said record, said end ofsaid stylus being immersed in a liquid developer, a counterelectrodedisposed on the face of said record medium opposite to the face which ismaintained in contact with the stylus and means to feed a signal to saidstylus indicative of the information to be recorded on said recordmedium.

2. The apparatus of claim 1 wherein means are provided for confining theliquid developer to an area surrounding said end of said stylus.

3. The apparatus of claim 1 wherein a source of potential is connectedbetween said stylus and said counterelectrode.

4. The apparatus of claim 3 in which at least one electro-opticaltransducer is provided for controlling the potential between said stylusand said counterelectrode and optics for imaging an optical signal onsaid electro-optical transducers.

5. The apparatus of claim 1 wherein there are a plurality of stylidisposed transversely of said record medium.

6. The apparatus of claim 5 wherein the styli are a plurality of finewires embedded in an insulating support.

7. The apparatus of claim l wherein the record medium is a tape.

8. A recording apparatus including at least one recording stylus, meansto move a rotary conducting drum having an insulating surface relativeto said stylus and to maintain one end of said stylus in physicalcontact with said drum, said end of said stylus being maintained in aliquid developer, means to feed an electrical signal, indicative of theinformation to be recorded on said drum, between said drum and saidstylus and means to contact a record medium to said drum to effect thetransfer of information from drum to record media.

l l l t

1. A recording apparatus including at least one recording stylus, meansto move a recording medium relative to said stylus and to maintain oneend of said stylus in physical contact with said record, said end ofsaid stylus being immersed in a liquid developer, a counterelectrodedisposed on the face of said record medium opposite to the face which ismaintained in contact with the stylus and means to feed a signal to saidstylus indicative of the information to be recorded on said recordmedium.
 2. The apparatus of claim 1 wherein means are provided forconfining the liquid developer to an area surrounding said end of saidstylus.
 3. The apparatus of claim 1 wherein a source of potential isconnected between said stylus and said counterelectrode.
 4. Theapparatus of claim 3 in which at least one electro-optical transducer isprovided for controlling the potential between said stylus and saidcounterelectrode and optics for imaging an optical signal on saidelectro-optical transducers.
 5. The apparatus of claim 1 wherein thereare a plurality of styli disposed transversely of said record medium. 6.The apparatus of claim 5 wherein the styli are a plurality of fine wiresembedded in an insulating support.
 7. The apparatus of claim 1 whereinthe record medium is a tape.
 8. A recording apparatus including at leastone recording stylus, means to move a rotary conducting drum having aninsulating surface relative to said stylus and to maintain one end ofsaid stylus in physical contact with said drum, said end of said stylusbeing maintained in a liquid developer, means to feed an electricalsignal, indicative of the information to be recorded on said drum,between said drum and said stylus and means to contact a record mediumto said drum to effect the transfer of information from drum to recordmedia.